The Collaborative International Dictionary of English v.0.48:

Ism \Ism\, n. [See ism, above.]
   A doctrine or theory; especially, a wild or visionary theory.
   --E. Everett.
   [1913 Webster]

         The world grew light-headed, and forth came a spawn of
         isms which no man can number.            --S. G.
                                                  Goodrich.
   Ismaelian

The Collaborative International Dictionary of English v.0.48:

-ism \-ism\ [F. -isme, or L. -ismus, Gr. ?.]
   A suffix indicating an act, a process, the result of an act
   or a process, a state; also, a characteristic (as a theory,
   doctrine, idiom, etc.); as, baptism, galvanism, organism,
   hypnotism, socialism, sensualism, Anglicism.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ism
    n 1: a belief (or system of beliefs) accepted as authoritative
         by some group or school [syn: doctrine, philosophy,
         philosophical system, school of thought, ism]